The present invention relates to a piezoelectric resonator held in a flat case suitable for automatic assembly.
A crystal resonator having a piezoelectric property, especially, a quartz resonator, has good electrical characteristics. In industrial fields which require very precise stability of an oscillation frequency, various types of conventional quartz resonators have been used in a variety of applications.
FIG. 1 is a sectional view of a conventional quartz resonator. A pair of lead-in conductors 1 extend inside through a base 2. The lead-in conductors 1 are held by and insulated from the base 2. The lead-in conductors 1 support two edge portions of a quartz plate 3. The quartz plate 3 is obtained by cutting a quartz material at a designed angle with respect to the crystallographic axes in accordance with a desired resonant mode. Electrodes are formed on a surface of the quartz plate 3 and are connected to the lead-in conductors 1. A cover 4 is placed on the quartz plate 3, and the edge of the cover 4 is hermetically welded by resistance welding to the edge of the base 2.
In the assembly process of the quartz resonator, connection of the lead-in conductors 1 to the quartz plate 3, fine adjustment of the resonant frequency, and sealing of the base 2 and the cover 4 are time-consuming. These operations are so elaborate that assembly cannot be performed by an automatic assembly machine.
Along with the increasing demand for compact electronic equipment, the size of semiconductor elements (e.g., ICs and LSIs) and circuit elements (e.g., resistors and capacitors) has been greatly decreased. In addition, the circuit elements tend to be mounted on single chips. These circuit element packages can be automatically mounted by an automatic assembly machine such as a parts feeder at predetermined positions on a printed circuit board, thereby improving the assembly efficiency.
However, the quartz resonator shown in FIG. 1 must be mounted on the printed circuit board in such a manner that the lead-in conductors 1 are inserted in the corresponding holes and are fixed by soldering or the like. As a result, an automatic assembly machine such as a parts feeder cannot be used, thereby degrading the assembly efficiency. In addition to this disadvantage, in this quartz resonator, a metal member used to hermetically seal the base 2 and the cover 4 by cold welding, for example, increases the material cost. The cover 4 has a greater height than that of the packaged circuit elements and is thus unsuitable for electronic equipment of high packing density.